Many methods of binarizing multilevel image data in order to output the data to a binary (bi-level) printer such as an ink-jet printer have been proposed. One binarization processing technique known in the art is the error diffusion method, which is a method of reproducing pseudo-halftones.
As disclosed in R. W. Floyd and L. Steinberg, “Adaptive algorithm for spatial grey scale”, SID Int. Sym. Digest of Tech. Papers, p. 36–37 (1975), the error diffusion method binarizes (converts to a maximum density level or maximum contrast level) multilevel image data of a pixel of interest, weights the error between the binarized level and the multilevel data that prevailed prior to binarization and adds the weighted error to the data of pixels neighboring the pixel of interest.
An example of a generally known apparatus which uses such a binarization method is a copier having a plurality of printing elements which print in accordance with thermal transfer or ink-jet technology. Another example is an electrophotographic copier which uses light-emitting elements such as LEDs.
Such copiers have a reading unit equipped with an optoelectric transducer such as a CCD and convert a document image to an electric signal by causing the reading unit to scan the document. Printing is performed by driving a plurality of printing elements on a printhead based upon the electric signal obtained by scanning, and the document image is reproduced on a printing medium such as printing paper by a well-known electrophotographic process or ink-jet technique.
A copier/MFP (multifunction printer) in which an image read by a reader can be printed directly by another printer via a network has been proposed in recent years.
FIG. 21 is a diagram illustrating the configuration of a network-connected image processing system.
As shown in FIG. 21, the system includes MFPs 2101, 2104 in which an image that has been read by a self-contained reader is printed out directly by each printer, a backbone network 2102, a computer 2103, a copier 2105 having a printing function and a printer 2016.
The computer 2103 is located in an environment in which each printer or the copier is capable of printing out images via the network 2102. Further, the MFP 2101 is capable of outputting an image read by its self-contained reader to the other printers or to the copier directly via the network 2101 without the intermediary of the computer 2103. Such output is possible irrespective of whether models are of the same type, such as the MFP 2104.
In such cases it is desirable for a read image to be transmitted upon being binarized in order to reduce the load on the network 2102. Accordingly, there are many cases in which use is made of error-diffusion-type binarization, which exhibits excellent tone reproduction and resolution.
Often, however, the reproducibility of isolated dots in electrophotography or the like is dependent upon the print engine. There are instances where an image having very poor tone reproduction is output, depending upon the printer, owing to variations in isolated-dot reproduction from one engine to another.
Further, the reproducibility of isolated dots depends greatly upon the process conditions, and dot reproducibility varies markedly owing changes in process conditions brought about by changes in the environment or change with time.
With error-diffusion-type binarization, there is a high likelihood that dots will be printed in isolated form and hence the effects brought about by discrepancies in the reproducibility of isolated dots is great.